Integrated circuit devices are commonly encapsulated to protect them from environmental hazards such as air, moisture, chemicals, and light, and to provide the integrated circuit with greater physical strength. Useful encapsulating materials include ceramics and polymers. Generally, encapsulating polymers include, for example, epoxies. Epoxies can include epoxy resins and thermosetting epoxy resins.
Integrated circuit devices include, for example semiconductor devices used in various electronic devices and optical devices. The semiconductor device can include many integrated circuit materials such as, at least one metal region, i.e., a metal line, bonding pad, and lead frame, at least one doped region, and at least one insulator layer formed on or in a semiconductor substrate. The semiconductor substrate is sometimes called a die. Often, the semiconductor device includes a heat sink.
Heat generated during operation can cause the integrated circuit materials to expand and/or contract. The amount that each integrated circuit material expands and/or contracts can be described by the coefficient of thermal expansion (“CTE”) of the particular material. And different materials have different CTE's. Composite materials, comprising one or more particular material, can expand and/or contract in volume and/or area as well. The expansion of the composite material can be described by the thermal expansion (“TE”) of the composite. The CTE's of the particular materials making up the composite can be combined in various ways, depending on the composite material in question, to yield a TE for the composite. For example, in some instances the TE of the composite can be a weighted average of the CTE's of each particular material in the composite. However, in other instances the CTE's of the particular materials making up the composite combine in other ways to yield the TE for the composite.
Problems often arise in integrated circuit devices, however, when the TE of materials making up the integrated circuit differ. One problem occurs at the interface of the semiconductor device and the encapsulating material. In particular, the thermal expansion of the semiconductor device (“TESD”) and the thermal expansion of the encapsulating material (“TEEM”) are not the same. As a result, these materials expand to different extents during operation and this can cause stress at the interface of these two materials. This stress often leads to cracking of the encapsulating material.
Accordingly, it would be useful to be able to match the TESD to the TEEM to prevent stress and reduce the negative effects of the stress.